Polymerase chain reaction (PCR) amplification has been used to identify retrovirus-like sequences in both multiple sclerosis (MS) patients and non-neurologic-control patients. Having used PCR to identify a novel endogenous retrovirus-like sequence on human brain DNA, we are now defining its tissue distribution and transcriptional activity. Genomic DNA was extracted from 12 autopsied brains of patients with multiple sclerosis and from eight without MS. PCR amplification of the DNA was performed, and radiolabeled fragments of cloned sequences were used to probe DNA complementary to RNA from different human organs, as well as from various animals. No correlation between PCR amplification and MS was found. The DNA insert cloned from PCR amplification products differed from any previously described sequence, and most likely represents an endogenous DNA sequence.